1. Field of the Invention
The invention relates to methods and apparatus for entry of characters on a computer keyboard, and specifically relates to methods and apparatus for selecting among various cases, or functions, controlled by individual keys.
2. The State of the Art
Typical manual typewriters have a multiplicity of type bars, each of which is mechanically linked to a key. Keys and type bars were made to do double duty by forming two characters on each type bar. A "shift" key then would reposition the entire array of type bars to determine whether the first or the second character on the type bars would be imprinted on the paper. The array of type bars was repositioned into the normal position by a spring when the shift key was released. Typing an upper-case key therefore required that the shift key first be depressed and second that the desired letter key be pressed while the shift key was still depressed. A separate "Shift Lock" key was often provided that would lock the type bars in the shifted position, and maintain them in that condition until the released by a separate act of the user.
Many features of todays computer keyboards are traceable to the characteristics of manual typewriters. Among these features is the QWERTY layout, and the requirement that a "shift" key be pressed and held while a character key is struck to generate an upper case character. Many keyboards also have one or more "Control" "Function" or "Alt" keys that change the function or character of a simultaneously struck key in a manner similar to the operation of the "Shift" key. The "Control, " "Function," "Alt," and "Shift" keys are all key-modifier keys, while the key having a function that is altered by the key-modifier key may be referred to as the modifiable key.
Generally, the key modifier keys are located at the sides of a keyboard where they are generally struck with the little finger. There are many people with limited hand mobility who find that operating these keys with the little finger is awkward. Additionally, the placement of key-modifier keys on many keyboards is such that simultaneous operation of key modifier keys and modifiable keys is difficult for those who have limited hand mobility or who type with one hand or with a mouthstick.
Northgate has sold a keyboard having an operating mode in which key-modifier keys alter the function of the first modifiable key struck following activation of the key-modifier key. The key-modifier is then automatically cleared such that the function of the second following modifiable key is not altered by the key-modifier key. The Northgate keyboard has the key-modifier keys located in the conventional locations, and has an operating mode in which the key-modifier keys behave conventionally.
Generally, keyboard keys respond only to motion or pressure applied to the key in a direction perpendicular to the plane of the keyboard. U.S. Pat. No. 4,680,577, issued to Straayer, et al., in 1986, describes a key having sensors that detect forces applied to the key in additional directions, or sideways, directions that are not perpendicular to the plane of the keyboard. Signals corresponding to the sideways forces detected by the key of the Straayer patent are used to manipulate the position of a cursor in place of a mouse.
The backspace key on a typical computer keyboard, such as the IBM 101-key layout, is not placed where it can be reached easily without requiring that the user remove his/her hands from their home positions on the keyboard.
A typical keyboard comprises an array of keys together with means for detecting a key that is pressed, and for identifying the specific key that is pressed. The means for detecting and identifying a key that is pressed may take many forms. On antique teletypes, detecting and identifying key presses is done mechanically. On many modern keyboards, key presses activate a switch associated with each key, the array of keys being scanned to detect and identify the particular key being pressed. Membrane switches are often used in keyboards. Switches are not necessary, some keyboards have magnets in the keys that, when the key is pressed, activate Hall-effect magnetic sensors associated with each key. Alternatively, key presses may be detected by devices that change resistance when under pressure.
Modern keyboards utilize an electronic device for scanning the array of keys to detect when a key is pressed and for generating a key code specific to the key pressed. This device may, but need not, be located on the same circuit board as the array of keys. This device may comprise dedicated electronic circuitry or may incorporate a small microprocessor programmed to scan the array. The microprocessor may also translate the key code into a standard encoded format and communicate, often serially, the translated code to a remote device.
Many electronic devices for scanning the array of keys operate by driving a first voltage on a row line, a line common to a plurality of key switches. There are usually more than one row line, the remaining row lines being resistively connected to a second voltage, as is a plurality of column lines. Each key switch in a row connects to a different column line. When a key switch is activated, and the associated row line is driven to the first voltage, the first voltage is coupled onto and may be sensed on the associated column line. Each key is therefore defined by the intersection of a row and a column. The keyboard is scanned by successively driving the first voltage on each of the row lines, while monitoring the column lines. This technique permits the keyboard scanning device to correctly identify at least two simultaneously active keys, possibly more depending upon their locations in the key array.
Electronically scanned keyboards also may have a diode in series with each of the key switches. The diodes allow the keyboard scanning device to correctly identify all active, or pressed, keys even if several keys are pressed simultaneously.